The invention relates to a fusible conductor for a fuse and also a fuse conductor and a fuse, as are used for interrupting excess currents such as occur for example as a consequence of short-circuits. Furthermore, it relates to a method of producing a fusible conductor and a fuse conductor.
It has long been known (see for example U.S. Pat. No. 3,705,373) to apply doping material, for example tin or solder consisting of tin and lead, at a doping point, usually approximately in the middle of the fusible conductor of a fuse, and consequently to lower the melting point and at the same time increase the resistance there, so that, when there is a small excess current, the fusible conductor melts through first at the doping point. U.S. Pat. No. 4,357,588 discloses a further fusible conductor of this type, which has a plurality of doping points following one another in the longitudinal direction, which are respectively provided on an arm of the fusible conductor, which is divided there by a longitudinal slit and is reduced in its cross section. At the doping point, the tin or solder combines with the conductor material, for example silver or copper, to form an intermetallic compound, that is to say it is dissolved to a greater or lesser degree in the conductor material.
However, compounds of this type are subjected to aging processes, in particular at somewhat elevated temperatures, as occur in this application area, and these processes may also change the electrical properties of the fusible conductor in an undesired or not clearly foreseeable way. In particular, the doping material may spread out by diffusion in the conductor material, so that finally the local delimitation of the doping points is broken down to a greater or lesser degree.
To interrupt a large excess current, the fusible conductors described in the aforementioned documents have cross-sectional constrictions which are produced by round punched cutouts and follow one another at equal intervals and at which the fusible conductor then rapidly melts through. However, the punched cutouts form weaknesses and increase the resistance of the fusible conductor considerably, so that relatively high power losses occur there.
In the document DE-C-624 633 a method for producing a fusible conductor is disclosed that is utilized in a fusible fuse. This fusible conductor has at least one doping point at which a doping material different from the conductor material is applied to the conductor material. As a conductor material there is used silver and as doping material tin. The at least one doping point has somewhat been stabilized by a heat treatment. At the at least one doping point an alloy of conductor material and doping material has formed. This alloy does obviously not show any homogeneous material distribution.
The invention is based on the object of specifying a fusible conductor of the generic type in which the at least one doping point exhibits stable and controllable properties. This object is achieved by an electrically conductive fusible conductor material with at least one doping point, at which the conductor material is mixed with a doping material different from it. which forms with the conductor material a mixture with a melting point which is lower than that of the conductor material, the mixture with the conductor material comprising at least one constituent of the conductor material and at least one constituent of the doping material combined in fixed stoichiometric ratios.
It is also intended to specify a fuse conductor which contains at least one fusible conductor of this type and, when there is a small excess current, is interrupted as far as possible over the entire length, and also a fuse which comprises a fusible conductor of this type or a fuse conductor of this type. Finally, it is intended to specify a method of producing a fusible conductor according to the invention.
The fusible conductor according to the invention has at least one doping point which is largely stable at the temperatures occurring. In particular, it remains localized. Its electrical properties and its melting point are not subject to any major changes or any major random fluctuations.
It may also have many doping points following one another at regular intervals, at which it melts through very rapidly when there is a large excess current, so that a high voltage, corresponding to the sum of all the arc voltages, builds up. In this respect, the doping points take the place of the cross-sectional constrictions of known fusible conductors, without the resistance being increased to the same extent however. The power loss is therefore much smaller.
The fuse conductor according to the invention is also provided with a burn-up element, which ignites when an ignition temperature, preferably lying just below the melting point of the doping point, is reached and burns while releasing heat. As a result, even when there are relatively small excess currents, an interruption of the fuse conductor over substantially the entire length is achieved and the excess current is rapidly interrupted. The fuse according to the invention has the benefits obtained by virtue of the properties of the fusible conductor according to the invention or the fuse conductor according to the invention.